Dynamic Self-Assembly of Magnetic Colloidal Particles

Abstract Dynamic self-assembly represent one of the most powerful tools in Nature to spontaneously organize a system on a hierarchy of different scales. Most of the processes at the nano/micro scale occur at very low Reynold’s number where inertia can be neglected. Creeping flow magnetic systems can be characterized by the Mason number. The Mason number measures the ratio between the viscous and the magnetic torque and is the main parameter governing the behavior of paramagnetic colloids investigated in this thesis. The work presented in this thesis explores new dynamic regimes of colloidal dynamics which occur when suddenly switching to high Mason numbers. In a static magnetic field the equilibrium structure of paramagnetic colloids are chains. At high Mason number in a rotating magnetic field the time averaged equilibrium conformation is a two dimensional cluster. By switching from a static to a rotating magnetic external field, we cause a transient dynamics from a static to the dynamic equilibrium state. The first question addressed in this thesis is: what is the physics that determines the transient folding pathway from one to the other equilibrium state? Dynamic magnetic fields were used by others to propel top down DNA-linked chains of paramagnetic colloids in a liquid. The second question asked is whether we can dynamically self-assemble swimmers taking a fully bottom up approach? The third question is: is it possible to assemble more complex dynamic patterns that lead to motion of the swimmers governed by more collective coupled hydrodynamics that goes beyond slender body theory of the linked chains? This thesis answers the three questions and contributes to the understanding of colloidal dynamics and self-assembly in dynamic magnetic fields in the regime of high Mason numbers. We explore two aspects of the dynamic self-assembly i.e. the transient kinetics between two dynamic self-assembled equilibria and the dynamically self-assembled propulsion of magnetic swimmers beyond slender body hydrodynamics. The thesis therefore aims at achieving magnetic control over the assembly of complex dynamic colloidal structures.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2013

Author dc:creator

• Casic, Nebojsa

Contributors dc:contributor

• Fischer, Thomas

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/129/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:129